
<!doctype html>
<html lang="en" class="no-js">
  <head>
    
      <meta charset="utf-8">
      <meta name="viewport" content="width=device-width,initial-scale=1">
      
      
      
      
      
        <link rel="next" href="get-started.html">
      
      
      <link rel="icon" href="assets/images/favicon.png">
      <meta name="generator" content="mkdocs-1.6.0, mkdocs-material-9.5.25">
    
    
      
        <title>{fmt}</title>
      
    
    
      <link rel="stylesheet" href="assets/stylesheets/main.6543a935.min.css">
      
      


    
    
      
    
    
      
        
        
        <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
        <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CRoboto+Mono:400,400i,700,700i&display=fallback">
        <style>:root{--md-text-font:"Roboto";--md-code-font:"Roboto Mono"}</style>
      
    
    
      <link rel="stylesheet" href="assets/_mkdocstrings.css">
    
      <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/10.7.2/styles/default.min.css">
    
      <link rel="stylesheet" href="fmt.css">
    
    <script>__md_scope=new URL(".",location),__md_hash=e=>[...e].reduce((e,_)=>(e<<5)-e+_.charCodeAt(0),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script>
    
      

    
    
    
  </head>
  
  
    <body dir="ltr">
  
    
    <input class="md-toggle" data-md-toggle="drawer" type="checkbox" id="__drawer" autocomplete="off">
    <input class="md-toggle" data-md-toggle="search" type="checkbox" id="__search" autocomplete="off">
    <label class="md-overlay" for="__drawer"></label>
    <div data-md-component="skip">
      
        
        <a href="#a-modern-formatting-library" class="md-skip">
          Skip to content
        </a>
      
    </div>
    <div data-md-component="announce">
      
    </div>
    
      <div data-md-color-scheme="default" data-md-component="outdated" hidden>
        
      </div>
    
    
      

<header class="md-header" data-md-component="header">
  <nav class="md-header__inner md-grid" aria-label="Header">
    <a href="index.html" title="{fmt}" class="md-header__button md-logo" aria-label="{fmt}" data-md-component="logo">
      
  
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54Z"/></svg>

    </a>
    <label class="md-header__button md-icon" for="__drawer">
      
      <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M3 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2Z"/></svg>
    </label>
    <div class="md-header__title" data-md-component="header-title">
      <div class="md-header__ellipsis">
        <div class="md-header__topic">
          <span class="md-ellipsis">
            {fmt}
          </span>
        </div>
        <div class="md-header__topic" data-md-component="header-topic">
          <span class="md-ellipsis">
            
              Home
            
          </span>
        </div>
      </div>
    </div>
    
    
      <script>var media,input,key,value,palette=__md_get("__palette");if(palette&&palette.color){"(prefers-color-scheme)"===palette.color.media&&(media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']"),palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent"));for([key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script>
    
    
    
      <label class="md-header__button md-icon" for="__search">
        
        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Z"/></svg>
      </label>
      <div class="md-search" data-md-component="search" role="dialog">
  <label class="md-search__overlay" for="__search"></label>
  <div class="md-search__inner" role="search">
    <form class="md-search__form" name="search">
      <input type="text" class="md-search__input" name="query" aria-label="Search" placeholder="Search" autocapitalize="off" autocorrect="off" autocomplete="off" spellcheck="false" data-md-component="search-query" required>
      <label class="md-search__icon md-icon" for="__search">
        
        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Z"/></svg>
        
        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12Z"/></svg>
      </label>
      <nav class="md-search__options" aria-label="Search">
        
        <button type="reset" class="md-search__icon md-icon" title="Clear" aria-label="Clear" tabindex="-1">
          
          <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M19 6.41 17.59 5 12 10.59 6.41 5 5 6.41 10.59 12 5 17.59 6.41 19 12 13.41 17.59 19 19 17.59 13.41 12 19 6.41Z"/></svg>
        </button>
      </nav>
      
    </form>
    <div class="md-search__output">
      <div class="md-search__scrollwrap" data-md-scrollfix>
        <div class="md-search-result" data-md-component="search-result">
          <div class="md-search-result__meta">
            Initializing search
          </div>
          <ol class="md-search-result__list" role="presentation"></ol>
        </div>
      </div>
    </div>
  </div>
</div>
    
    
      <div class="md-header__source">
        <a href="https://github.com/fmtlib/fmt" title="Go to repository" class="md-source" data-md-component="source">
  <div class="md-source__icon md-icon">
    
    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 6.5.2 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2024 Fonticons, Inc.--><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"/></svg>
  </div>
  <div class="md-source__repository">
    GitHub
  </div>
</a>
      </div>
    
  </nav>
  
</header>
    
    <div class="md-container" data-md-component="container">
      
      
        
          
            
<nav class="md-tabs" aria-label="Tabs" data-md-component="tabs">
  <div class="md-grid">
    <ul class="md-tabs__list">
      
        
  
  
    
  
  
    <li class="md-tabs__item md-tabs__item--active">
      <a href="index.html" class="md-tabs__link">
        
  
    
  
  Home

      </a>
    </li>
  

      
        
  
  
  
    <li class="md-tabs__item">
      <a href="get-started.html" class="md-tabs__link">
        
  
    
  
  Get Started

      </a>
    </li>
  

      
        
  
  
  
    <li class="md-tabs__item">
      <a href="api.html" class="md-tabs__link">
        
  
    
  
  API

      </a>
    </li>
  

      
        
  
  
  
    <li class="md-tabs__item">
      <a href="syntax.html" class="md-tabs__link">
        
  
    
  
  Syntax

      </a>
    </li>
  

      
    </ul>
  </div>
</nav>
          
        
      
      <main class="md-main" data-md-component="main">
        <div class="md-main__inner md-grid">
          
            
              
                
              
              <div class="md-sidebar md-sidebar--primary" data-md-component="sidebar" data-md-type="navigation" hidden>
                <div class="md-sidebar__scrollwrap">
                  <div class="md-sidebar__inner">
                    


  


  

<nav class="md-nav md-nav--primary md-nav--lifted md-nav--integrated" aria-label="Navigation" data-md-level="0">
  <label class="md-nav__title" for="__drawer">
    <a href="index.html" title="{fmt}" class="md-nav__button md-logo" aria-label="{fmt}" data-md-component="logo">
      
  
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54Z"/></svg>

    </a>
    {fmt}
  </label>
  
    <div class="md-nav__source">
      <a href="https://github.com/fmtlib/fmt" title="Go to repository" class="md-source" data-md-component="source">
  <div class="md-source__icon md-icon">
    
    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 6.5.2 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2024 Fonticons, Inc.--><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"/></svg>
  </div>
  <div class="md-source__repository">
    GitHub
  </div>
</a>
    </div>
  
  <ul class="md-nav__list" data-md-scrollfix>
    
      
      
  
  
    
  
  
  
    <li class="md-nav__item md-nav__item--active">
      
      <input class="md-nav__toggle md-toggle" type="checkbox" id="__toc">
      
      
        
      
      
      <a href="index.html" class="md-nav__link md-nav__link--active">
        
  
  <span class="md-ellipsis">
    Home
  </span>
  

      </a>
      
    </li>
  

    
      
      
  
  
  
  
    <li class="md-nav__item">
      <a href="get-started.html" class="md-nav__link">
        
  
  <span class="md-ellipsis">
    Get Started
  </span>
  

      </a>
    </li>
  

    
      
      
  
  
  
  
    <li class="md-nav__item">
      <a href="api.html" class="md-nav__link">
        
  
  <span class="md-ellipsis">
    API
  </span>
  

      </a>
    </li>
  

    
      
      
  
  
  
  
    <li class="md-nav__item">
      <a href="syntax.html" class="md-nav__link">
        
  
  <span class="md-ellipsis">
    Syntax
  </span>
  

      </a>
    </li>
  

    
  </ul>
</nav>
                  </div>
                </div>
              </div>
            
            
          
          
            <div class="md-content" data-md-component="content">
              <article class="md-content__inner md-typeset">
                
                  

  
  


<h1 id="a-modern-formatting-library">A modern formatting library</h1>
<div class="features-container">

<div class="feature">
<h2>Safety</h2>
<p>
  Inspired by Python's formatting facility, {fmt} provides a safe replacement
  for the <code>printf</code> family of functions. Errors in format strings,
  which are a common source of vulnerabilities in C, are <b>reported at
  compile time</b>. For example:

  <pre><code class="language-cpp"
  >fmt::format("{:d}", "I am not a number");</code></pre>

  will give a compile-time error because <code>d</code> is not a valid
  format specifier for strings. APIs like <a href="api/#format">
  <code>fmt::format</code></a> <b>prevent buffer overflow errors</b> via
  automatic memory management.
</p>
<a href="api#compile-time-checks">→ Learn more</a>
</div>

<div class="feature">
<h2>Extensibility</h2>
<p>
  Formatting of most <b>standard types</b>, including all containers, dates,
  and times is <b>supported out-of-the-box</b>. For example:

  <pre><code class="language-cpp"
  >fmt::print("{}", std::vector{1, 2, 3});</code></pre>

  prints the vector in a JSON-like format:

  <pre><code>[1, 2, 3]</code></pre>

  You can <b>make your own types formattable</b> and even make compile-time
  checks work for them.
</p>
<a href="api#udt">→ Learn more</a>
</div>

<div class="feature">
<h2>Performance</h2>
<p>
  {fmt} can be anywhere from <b>tens of percent to 20-30 times faster</b> than
  iostreams and <code>sprintf</code>, especially for numeric formatting.

<a href="https://github.com/fmtlib/fmt?tab=readme-ov-file#benchmarks">
<img src="perf.svg">
</a>

  The library <b>minimizes dynamic memory allocations</b> and can optionally
  <a href="api#compile-api">compile format strings</a> to optimal code.
</p>
</div>

<div class="feature">
<h2>Unicode support</h2>
<p>
  {fmt} provides <b>portable Unicode support</b> on major operating systems
  with UTF-8 and <code>char</code> strings. For example:

  <pre><code class="language-cpp"
  >fmt::print("Слава Україні!");</code></pre>

  will be printed correctly on Linux, macOS, and even Windows console,
  irrespective of the codepages.
</p>
<p>
  The default is <b>locale-independent</b>, but you can opt into localized
  formatting and {fmt} makes it work with Unicode, addressing issues in the
  standard libary.
</p>
</div>

<div class="feature">
<h2>Fast compilation</h2>
<p>
  The library makes extensive use of <b>type erasure</b> to achieve fast
  compilation. <code>fmt/base.h</code> provides a subset of the API with
  <b>minimal include dependencies</b> and enough functionality to replace
  all uses of <code>*printf</code>.
</p>
<p>
  Code using {fmt} is usually several times faster to compile than the
  equivalent iostreams code, and while <code>printf</code> compiles faster
  still, the gap is narrowing.
</p>
<a href=
"https://github.com/fmtlib/fmt?tab=readme-ov-file#compile-time-and-code-bloat">
→ Learn more</a>
</div>

<div class="feature">
<h2>Small binary footprint</h2>
<p>
  Type erasure is also used to prevent template bloat, resulting in <b>compact
  per-call binary code</b>. For example, a call to <code>fmt::print</code> with
  a single argument is just <a href="https://godbolt.org/g/TZU4KF">a few
  instructions</a>, comparable to <code>printf</code> despite adding
  runtime safety, and much smaller than the equivalent iostreams code.
</p>
<p>
  The library itself has small binary footprint and some components such as
  floating-point formatting can be disabled to make it even smaller for
  resource-constrained devices.
</p>
</div>

<div class="feature">
<h2>Portability</h2>
<p>
  {fmt} has a <b>small self-contained codebase</b> with the core consisting of
  just three headers and no external dependencies.
</p>
<p>
  The library is highly portable and requires only a minimal <b>subset of
  C++11</b> features which are available in GCC 4.9, Clang 3.4, MSVC 19.10
  (2017) and later. Newer compiler and standard library features are used
  if available, and enable additional functionality.
</p>
<p>
  Where possible, the output of formatting functions is <b>consistent across
  platforms</b>.
</p>
</p>
</div>

<div class="feature">
<h2>Open source</h2>
<p>
  {fmt} is in the top hundred open-source C++ libraries on GitHub and has
  <a href="https://github.com/fmtlib/fmt/graphs/contributors">hundreds of
  all-time contributors</a>.
</p>
<p>
  The library is distributed under a permissive MIT
  <a href="https://github.com/fmtlib/fmt#license">license</a> and is
  <b>relied upon by many open-source projects</b>, including Blender, PyTorch,
  Apple's FoundationDB, Windows Terminal, MongoDB, and others.
</p>
</div>

</div>







  
  




  



                
              </article>
            </div>
          
          
<script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script>
        </div>
        
          <button type="button" class="md-top md-icon" data-md-component="top" hidden>
  
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8v12Z"/></svg>
  Back to top
</button>
        
      </main>
      
        <footer class="md-footer">
  
  <div class="md-footer-meta md-typeset">
    <div class="md-footer-meta__inner md-grid">
      <div class="md-copyright">
  
  
</div>
      
    </div>
  </div>
</footer>
      
    </div>
    <div class="md-dialog" data-md-component="dialog">
      <div class="md-dialog__inner md-typeset"></div>
    </div>
    
    
    <script id="__config" type="application/json">{"base": ".", "features": ["navigation.tabs", "navigation.top", "toc.integrate"], "search": "assets/javascripts/workers/search.b8dbb3d2.min.js", "translations": {"clipboard.copied": "Copied to clipboard", "clipboard.copy": "Copy to clipboard", "search.result.more.one": "1 more on this page", "search.result.more.other": "# more on this page", "search.result.none": "No matching documents", "search.result.one": "1 matching document", "search.result.other": "# matching documents", "search.result.placeholder": "Type to start searching", "search.result.term.missing": "Missing", "select.version": "Select version"}, "version": {"provider": "mike"}}</script>
    
    
      <script src="assets/javascripts/bundle.081f42fc.min.js"></script>
      
        <script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/10.7.2/highlight.min.js"></script>
      
        <script src="fmt.js"></script>
      
    
  </body>
</html>